The limulus test was found to be nonspecific in attempting to determine pyogenic arthritis in humans. A very significant correlation was found between a positive limulus test and an elevated neutrophil count. It may be that neutrophils or a product of neutrophils can cause a positive limulus test. Thrombin, esterase and poly I poly C were found to cause a positive limulus assay. A nephelometric method for performing the limulus assay is being studied.